1. Field of the Invention
The present invention relates to a piston cooling jet that cools a piston of an engine by spraying oil toward the back surface of the piston.
2. Description of Related Art
A piston cooling jet is attached to a cylinder block of an engine. The piston cooling jet communicates with a main oil gallery of the cylinder block. The main oil gallery forms a part of an oil circulation circuit of the engine. The piston cooling jet is provided with a hydraulic valve mechanism.
When the hydraulic pressure of oil in the main oil gallery is equal to or more than a predetermined threshold, the hydraulic valve mechanism of the piston cooling jet is opened. This causes oil in the main oil gallery to be sprayed toward the back surface of the piston by the piston cooling jet. The spray of oil cools the piston.
During hot times when the piston is at a high temperature, the piston is preferably cooled by the piston cooling jet. During cold times when the piston is at a low temperature, however, it is necessary to warm the piston immediately. Therefore, cooling the piston using the piston cooling jet during cold times may hinder a rise in temperature of the piston. For such reason, oil is preferably not sprayed during cold times. However, the hydraulic valve mechanism of the piston cooling jet according to the related art is opened and closed in accordance with the hydraulic pressure in the main oil gallery, rather than the temperature of the engine. Therefore, the piston cooling jet may be actuated even during cold times.
In view of such issues, Japanese Patent Application Publication No. 2011-12650 (JP 2011-12650 A) discloses a piston cooling jet including a hydraulic-pressure valve mechanism section and an oil-temperature valve mechanism section. In the piston cooling jet according to JP 2011-12650 A, the hydraulic-pressure valve mechanism section switches the oil spraying state in accordance with the hydraulic pressure of oil. Meanwhile, the oil-temperature valve mechanism section switches the oil spraying state in accordance with the temperature of oil.
The hydraulic-pressure valve mechanism section uses one coil spring. Meanwhile, the oil-temperature valve mechanism section uses two coil springs. The two coil springs of the oil-temperature valve mechanism section are arranged in series along the direction of a passage of oil via a closure member. Of the two coil springs, the coil spring on the upper side (upstream side) is a shape memory spring made of a shape memory alloy. The urging force of the coil spring is varied in accordance with the temperature. Of the two coil springs, the coil spring on the lower side (downstream side) is a bias spring.
During cold times, the urging force of the bias spring is larger than that of the shape memory spring. Therefore, the passage of oil is closed. Thus, spraying of oil is stopped.
During hot times, on the other hand, the urging force of the shape memory spring is larger than that of the bias spring. Therefore, the passage of oil is opened. Thus, spraying of oil is allowed.
According to the piston cooling jet described in JP 2011-12650 A, however, a total of three coil springs are necessary. This complicates the structure of the piston cooling jet. This also increases the number of components.
According to the piston cooling jet described in JP 2011-12650 A, in addition, it is necessary that one of the three coil springs should be made of a shape memory alloy. This increases the manufacturing cost of the piston cooling jet.
In view of such issues, the present inventor has developed a novel piston cooling jet. It should be noted, however, that the piston cooling jet is not one of those according to the related art.
The piston cooling jet includes a housing, a valve, a leak gap, and a coil spring. The valve is housed in the housing so as to be reciprocally movable. The valve partitions the inside of the housing into a pressure receiving chamber on the upper side and a pressure chamber on the lower side to serve as a movable partition. The valve is provided with an orifice. The coil spring is housed in the pressure chamber. The coil spring urges the valve upward. The pressure receiving chamber communicates with a main oil gallery of the engine. The leak gap is disposed downstream of the pressure chamber. The leak gap communicates with the outside. Oil in the main oil gallery flows to the outside sequentially through the pressure receiving chamber, the orifice, the pressure chamber, and the leak gap.
The piston cooling jet includes the orifice provided upstream of the pressure chamber, and the leak gap provided downstream of the pressure chamber. This allows the internal pressure of the pressure chamber to be varied in accordance with the temperature and the hydraulic pressure of oil. Moreover, using the variations in the internal pressure allows the valve to be reciprocally moved between a valve open position and a valve closed position.
Thus, according to the novel piston cooling jet, oil spray control can be executed in accordance with the temperature and the hydraulic pressure of oil by the single coil spring. This simplifies the structure of the piston cooling jet. This also reduces the number of components. According to the novel piston cooling jet, in addition, it is not necessary that the coil spring should be made of a shape memory alloy. This reduces the manufacturing cost of the piston cooling jet.
In the case of the novel piston cooling jet, in order to control the internal pressure of the pressure chamber, it is necessary to secure an oil path (a path that leads from the main oil gallery to the outside by way of the pressure chamber). However, oil may contain, as mixed therein, foreign matter such as sludge, abrasion powder, dust, and machining powder produced during engine manufacture, for example. If the foreign matter clogs the oil path, oil does not flow smoothly. This makes it difficult to control the internal pressure of the pressure chamber.
In such a case, from the viewpoint of suppressing a rise in temperature of the piston, the piston cooling jet is preferably in a valve open state in which oil is sprayed toward the piston, rather than in a valve closed state in which oil is not sprayed toward the piston.